Trajectory Tracking Control Of Robotic Manipulator Based On Improved Fractional-order Terminal Sliding Mode

The purpose of the trajectory tracking control of the manipulator is that the error of the system is always kept to a minimum when the manipulator moves according to the desired trajectory,even if there is interference.Therefore,the trajectory tracking control with high precision and fast response is the research focus of the manipulator.Position tracking of free-space manipulator,because the terminal sliding mode control introduces nonlinear function into the design of its sliding surface,the system error can converge in finite time,which is deeply concerned by scholars in the control direction of the manipulator.For the control of mission space manipulator,there are many researches on linear sliding mode control,but it can only ensure the asymptotic convergence of tracking error,but not its finite time convergence.The fractional terminal sliding mode integrates the fractional calculus theory and the terminal sliding mode control theory,compared with the ordinary terminal sliding mode control,the inheritance of fractional calculus and"infinite memory" characteristics are used to further improve the tracking speed and control accuracy of the control system.However,the ordinary fractional terminal sliding mode has the problems of singularity and buffeting,and the convergence speed and control accuracy still need to be improved.Considering the above fractional-order terminal sliding mode control problem of robotic manipulators,fractional-order non-singular fast terminal sliding mode tracking control strategies are studied,based on time delay estimation,fuzzy control,adaptive theory and other techniques.The main research work is stated as follows:For the position tracking control of free space manipulator,an adaptive fractionalorder non-singular fast terminal sliding mode scheme based on time delay estimation is proposed for the control of robotic manipulators.A new fractional-order non-singular fast terminal sliding mode surface with a continuous switch item is designed to ensure good performance,such as fast finite-time convergence,high precision and being nonsingular.The TDE element is used to estimate the robot's unknown dynamic parameters and external disturbances.The Lyapunov stability theory is used to prove the finite-time stability of the control system.The proposed control algorithm is applied to a two-link robotic manipulator and the comparative results verify the effectiveness and superiority of the proposed control approach in comparison with existing control methods.For the simultaneous control of position and force of the manipulator in the workspace,a fractional-order non-singular fast terminal sliding mode impedance control scheme based on fuzzy control is designed.For position tracking,a new fractionalorder non-singular terminal sliding surface is established according to the position and velocity errors in cartesian coordinate system,and the friction force and external interference in the dynamic equation of the manipulator are compensated by fuzzy system approximation.Finally,the fast finite time convergence of position tracking error is realized.Based on the analysis of the contact force,a spring damping system which can be equivalent to the mechanical arm and the environment model is designed to control the contact force by controlling the change of position error.The simulation results of a two-link manipulator constrained by resistance show that the proposed control scheme is effective.